Electron-emission material



v Patented May 27, 1930 UNITED .STATES PATENT OFFICE.

HARVEY c. BENTSGHLER, JOHN .W. MARDEN, AND CLAYTON '1'. ULBEY, 61m

ORANGE, NEW JERSEY, ASSIGNORS TO WESTINGHOUSE LAMP COMPANY, A COB- PORATION OF PENNSYLVANIA ELECTRON-EMISSION MATERIAL Original application filed June 25, 1921, Serial No. 480,301. Divided and this application filed December 23, 1922. Serial No.-608,784.

This application is a division of our application, Serial No. 480,301, filed June 25, 1921, for an improvement in Electron emission ma terial, and assigned to the \Vestinghouse Lamp Company.

This invention relates to electron-emission material and, more particularly, to refractory metals and alloys which have characteristics making them especially desirable for electron-emission.

Vacuum tubes for various purposes, such as for detectors and oscillators in wireless receiving and sending apparatus, are of considerable importance, and the material from which the cathodes of such tubes are constructed generally determines the life and utility thereof. It is desirable that the cathode has ahigh electron emission, and it should be so designed as to be operated at as low temperature as possible in order to avoid vaporization of the material thereof, since such vaporization causes rapid deterioration of the cathode and decreases the life of the tube. The use of lower temperatures also resuljts in a higher electrical eiiiciency of the tu e.

Various types of cathodes and various kinds of materials therefore have been proposed and, although they are fairly success ful, the efficiency and operating characteristics thereof are not entirely satisfactory be.

cause of the high operating temperatures. It has been proposed to utilize tungsten filaments, or metal coated with various oxides, such as oxides of calcium, strontium, barium or the like. In order to obtain a suitable electron emission from tungsten filaments, it is necessary to operate the cathode at such high temperature that the life of the bulb is rela tively short and the bulb becomes blackened very rapidly. The oxide coated filaments disintegrate and develop hot spots, causing the burning out of the cathode at such spots.

Our invention contemplates the production of an electron-emission material which is far superior to any proposed heretofore, which may be 'operated at much lower temperatures, giving a greater electron emission and having a higher efliciency.

In practlcing our invention, we utilize rare metals. WVe have found that uranium has an electron emission at comparatively low temperatures which is equal to the electron emission of tungsten at temperatures of about 325 C. higher.

Our mater al consists essentially'of the refractory metal uranium, which has a high electron-emi'ssive power and, in order to modify its propertiesto make it more suitable for filaments, we may alloy it with another metal, for instance, tungsten, to improve its working properties.

The accompanying drawing illustrates curves obtained by plotting the milliamperes of current produced by one square centimeter of electron-emission material as ordinates, against temperatures as abscissa.

It will be seen that the curve for uranium is of approximately the same type as that for tungsten with the exception that it is placed at a point at about 325 C. lower than the tungsten curve. The uranium materials give electron emissions at about 17 00 C. of the same order as tungsten at about"2025 C.

Alloys of various refractory rare metals also show high electron emission, particularly the uranium alloys. For instance, a uranium alloy of a composition containing 7 %uranium. and 93% tungsten shows an electron emission equal to that of a filament of pure uranium. An alloy. of 25% uranium and 75% tungsten also shows an electron emission substantially that of uranium. Alloys of uranium with metals, such as tungsten, molybdenum or tantalum, all show electron emissions superior to that of the alloying metal, usually in the neighborhood of the electron emission of uranium.

We conclude, from these phenomena, that the electron-emitting power of a substance containing two or more elements is primarily a property of the electron emission of the element which is active at the lower temperatures, although this property may be modified to some extent by the molecular or physical structure of the material.

We claim as our invention:

1. Material suitable for use as' an electron emitter in electron discharge devices comprised of a. refractory metal body containing approximately 93' per cent tungstenand approximately 7 per cent uranium.

- 2. In an electron discharge device employ ing a thermionic cathode and at least one operating electrode, a refractory hot cathode comprised of tungsten containing approximately 7-per cent uranium alloyed therewith. v

In testimony whereof, we have hereunto- 0 subscribed our names this 22nd day of December, 1922. HARVEY C. RENTSCHLER. JOHN W. MARDEN. CLAYTON T; ULREY. 

